If we can miniaturize nuclear reactors to the point that they can be drop-in replacements for batteries, then we can potentially run our electronics, appliances, machinery, vehicles standalone for decades without refuel/recharge.
Nuclear reactors can't generally be scaled down too far. The shielding requirements are about 4 ft of concrete on all sides, basically as a minimum. You can use pure-alpha decay radioactive isotopes as long lasting heat sources with a thermionic to make a 100W battery that last ~100 years. These are used in space probes like Voyager 1/2, Cassini, and Mars rovers like Curiosity and (soon) Perseverance. It used to also be used in pacemakers and soviet arctic light-houses.
The material is expensive (though it could be made much cheaper if a big market showed up), but more seriously it's a radiological hazard. Someone could disassemble such a thing and blow it up on a busy street with conventional explosives and cause a massive radiophobia-induced panic. You don't want to inhale a strong alpha-emitter.
I had heard these used Strontium(/Yttrium)-90 (β), but I might have been misinformed. Do you know where I can find more information about this subject?
Betavoltaic cells get outperformed by coin cells and RTGs by solar panels in most applications. There are some niche space applications, but not much else.
